* include/ruby/st.h (st_table): Added comment why we need __extension__.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@30757 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,7 @@
+Wed Feb  2 00:30:43 2011  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
+
+	* include/ruby/st.h (st_table): Added comment why we need __extension__.
+
 Tue Feb  1 20:45:44 2011  Tanaka Akira  <akr@fsij.org>
 
 	* enc/encdb.c: parenthesize macro arguments.

include/ruby/st.h

@@ -79,6 +79,15 @@ struct st_table {
     st_index_t num_bins;
     unsigned int entries_packed : 1;
 #ifdef __GNUC__
+    /*
+     * C spec says,
+     *   A bit-field shall have a type that is a qualified or unqualified
+     *   version of _Bool, signed int, unsigned int, or some other
+     *   implementation-defined type. It is implementation-defined whether
+     *   atomic types are permitted.
+     * In short, long and long long bit-field are implementation-defined
+     * feature. Therefore we want to supress a warning explicitly.
+     */
     __extension__
 #endif
     st_index_t num_entries : ST_INDEX_BITS - 1;